(NaturalNews) The first large-scale study to look at the connection between mobile phone use in pregnancy and later behavioral problems in children has overwhelmingly come back with a finding that such phone use places undeveloped babies at risk.

Researchers from the University of California-Los Angeles (UCLA) and the University of Aarhus, Denmark surveyed 13,519 women who had given birth in Denmark in the late 1990s about their mobile phone use habits while pregnant, and their children's use of the phones up until the age of seven. Due to the fact that cell phone use was less widespread a decade ago, about half of the women in the study had not used the phones while pregnant, or used them only infrequently.

Women who used handsets two or three times per day while pregnant were 54 percent more likely to give birth to children who developed behavioral problems by the time they reached school age than women who did not use them. The risk of behavioral problems increased along with the mother's mobile phone use during pregnancy.

If children used the phones themselves while very young, they were 80 percent more likely to suffer behavioral difficulties, 25 percent more likely to suffer from emotional problems, 34 percent more likely to have trouble relating to their peers, 35 percent more likely to be hyperactive and 49 percent more likely to have conduct problems than children who did not use mobile phones.

The findings were published in the journal Epidemiology.

One of the lead researchers, Leeka Kheifets of UCLA, had previously stated in writing that there was "no consistent evidence of a causal relationship between exposure to radiofrequency fields [including those from mobile phones] and any adverse health effect." A well-known skeptic of the connection between mobile phone use and health or behavioral problems, Kheifets admitted to being surprised by the current study's findings.

The researchers attempted to demonstrate that some other confounding factor - such as smoking during pregnancy, socioeconomic status or a family history of mental illness - had caused the behavioral effects observed. But when they corrected for these factors, the contribution of mobile phones actually became statistically stronger.

Saying that they did not know of any biological mechanism by which mobile phones could cause behavioral problems, the researchers urged that their results "should be interpreted with caution." They also suggested that there might be some correlation between cellular phone use and some other factor that leads to behavioral difficulties - such as neglect by a mother that spends too much time on the phone.

But they conceded that "if [the results] are real they would have major public health implications."

Sam Millham of the Mount Sinai School of Medicine and the University of Washington School of Public Health, said that he is certain the study results are accurate. Recent research conducted in Canada on pregnant rats demonstrated that radiation similar to that from mobile phones caused structural changes to the brains of the fetuses, he said.

Millham is considered a pioneer in researching the connection between mobile phone use and negative health effects.

The study's results came not long after the Russian National Committee on Non-Ionizing Radiation Protection released new warnings about the use of mobile phones by pregnant women and children. Use of cellular phones by children can lead to short-term "disruption of memory, decline of attention, diminishing learning and cognitive abilities, increased irritability," while long-term use can cause "depressive syndrome [and] degeneration of the nervous structures of the brain."

The committee counseled pregnant women and children to limit their exposure to mobile phones, warning that the health risk from the devices "is not much lower than the risk to children's health from tobacco or alcohol."